Initiation of in situ combustion in a carbonaceous stratum



Nov. 6, 1962 A. R. scHLElcHER INITIATION OF' IN SITU COMBUSTION IN A CARBONACEOUS STRATUM Filed Jan. 24, 1958 n. 0R TAR FORMATION INJECTION r 0R PRoDucTmN f-/|4- DEN ERBUR OIL OR TAR FORMATION INVENTOR. v A. R. SCHLEICHER BYav-v# United States Patent iiice 3,062,282 Patented Nov. 6, 1962 3,662,262 IATIQN F EN SlTU CGMBUSTGN IN A CARBNACEUS STRATUM Arthur R. Schleicher, Urbana, lll., assiguor to Phillips Petroleum Company, a corporation of Delaware Filed Eau. 24, 1958, Ser. No. 71),908 13 Claims. (Cl. 16o-1l) This invention relates to `a process for initiating in situ combustion in a carbonaceous stratus and to the recovery of hydrocarbons therefrom.

In situ combustion in the recovery of hydrocarbons from underground strata containing carbonaceous material is becoming more prevalent in the petroleum industry. 11n this technique of production, combustion is initiated in the carbonaceous stratum and the resulting cornbustion zone is caused to move thru the stratum by either inverse or direct air drive whereby the heat of combustion of a substantial proportion of the hydrocarbon in the stratum drives out and usually upgrades a substantial proportion of the remaining hydrocarbon material.

The ignition `of carbonaceous material in a stratum around a borehole therein followed by injection of air thru the ignition -borehole and recovery of product hydrooarbons and combustion gas thru another borehole in the stratum is a direct air drive process for effecting in situ combustion and recovery of hydrocarbons from the stratum. In this type of operation the stratum usually plugs in front of the combusion zone because a heavy viscous fluid bank collects in the stratum in Iadvance of the combustion zone which prevents movement of air to the combustion process. To overcome this difficulty and permit the continued progress of the combustion zone thru the stratum, inverse air injection has been resorted to. By this technique, a combustion zone is established around an ignition borehole by any suitable means and air is fed thru the stratum to the combustion zone from one or more surrounding boreholes.

Field tests have shown that with most strata it is easier to initiate in situ combustion utilizing direct injection of air or other free-oXygen-containing gas thru the heated ignition borehole into the stratum to be ignited and, except for the plugging of the formation during initial combustion or shortly thereafter by the melted tar highly viscous hydrocarbon material which tends to congeal and plug the formation when the viscous liquid reaches a cooler zone in advance of the combustion front, direct Iair injection Would usually be more desirable. When starting a fire in the stratum by inverse air injection into the hot ignition borehole utilizing a downhole heater to heat the stratum, melted tar or other viscous hydrocarbon is driven into the ignition borehole and burns therein with damage to the downhole equipment. The instant invention is concerned with a method or process for initiating combustion in a carbonaceous stratum containing meltable tar or highly viscous hydrocarbon material which avoids the problems enumerated above.

Accordingly, it is an object of the invention to provide a novel and improved process for initiating in situ combustion in a permeable carbonaceous stratum containing tar or highly viscous hydrocarbon material. Another object is to provide -a process for initiating in situ combustion by direct air injection which avoids plugging of the `stratum due to the congealing of iluidized heavy hydrocarbon material in the stratum in advance of the combustion zone. Other objects of the invention will become apparent upon consideration of the accompanying disclosure.

A broad aspect of the invention comprises heating a section of the stratum -to be ignited around an ignition borehole therein to a temperature below the ignition temperature of the carbonaceous material but sufficiently high to render more fluid and less viscous the heavy hydrocarbon material in the stratum and passing a flushing fluid thru the hot `section of the stratum so as to drive the heavy liquid hydrocarbon therefrom and removing this hydrocarbon from the formation and thereafter igniting the remaining carbonaceous material in the hot sect-ion of stratum so as to establish in situ combustion therein. The section of stratum immediately surrounding the ignition borehole is heated by any suitable means such 4as by a downhole gas or electric heater, or by means of a pyrotechnic, and ushing fluid is passed thru the hot section either from the ignition borehole to one or more surround-ing boreholes which may be in a ring pattern, such 'as a 5-spot or 7-spot well pattern, or thru the boreholes in the ring so that the heavy hydrocarbon material is flushed into the ignition borehole. In-line ignition boreholes may be utilized with in-line boreholes on either side of the line of ignition boreholes. The ushing uid may comprise -air or an inert gas such -as nitrogen. CO2 or combustion gas may .also be utilized and the gas may be preheated to increase the effectiveness of the ilushing step. Other flushing fluids include light hydrocarbons such as the normally gaseous hydrocarbons ethane, propane, butane, and the corresponding olens as well as normally liquid hydrocarbons such as benzene, gasoline, etc.

When utilizing liquid hydrocarbons or other liquid solvents for tar and semi-solid hydrocarbon materials in the stratum as flushing iluid, the liquid is forced into the stratum around the ignition borehole either thru the ignition borehole or thru boreholes positioned in a ring pattern Iaround the ignition borehole and closely spaced thereto, preferably, within the range of 2 to 10 feet. Another method of operation comprises injecting flushing liquid into the stratum thru an ignition borehole by pressurizing the same so as to prive the solvent into the stratum a short distance in the range of 2 to 10 feet and then depressurizing the ignition borehole and driving the solvent and dissolved tar back into the ignition borehole by injecting gas into the surrounding boreholes. The solvent should not be used so as to completely remove all tar from the section of stratum around the ignition borehole but should leave enough for combustion fuel.

ln any event, after removing melted )and/or dissolved tar and heavy hydrocarbon from the `section of stratum around the ignition borehole, this section of stratum is heated to the ignition temperature of the residual hydrocarbon material and the hot stratum is then contacted with an oxygen-containing gas such as oxygen-enriched air or pureoxygen so as to ignite and burn the carbonaceous material therein and establish in situ combustion in the stratum. After ignition and establishment of in situ combustion, the combustion Zone is preferably driven or advanced thru the stratum outwardly from the ignition borehole by inverse air injection thru surrounding boreholes. The surrounding boreholes may be spaced anywhere from a few feet to a thousand feet or more from the Iignition borehole; however the closely surrounding bore holes utilized in the ilushing process are preferably spaced a distance in the range of 2 to 25 feet from the ignition borehole.

The preheating of the section of stratum surrounding the ignition borehole in which in situ combustion is to be initiated may be effected entirely by hot air or other hot gas injected into the formation either thru the ignition borehole or thru the boreholes closely spaced around the ignition borehole. In this manner the section of stratum is raised in temperature so as to melt and/ or render more iluid the hydrocarbon material in the section of stratum and as it is rendered more fluid, it is driven either into the ignition borehole or into the surrounding boreholes, depending upon the injection point or points. When using air as the flushing and heating gas, the temperature of the section of stratum should not be raised to the ignition temperature of the carbonaceous material until suicient heavy hydrocarbon is removed from the section of stratum to avoid the possibility of plugging when ignition by direct air injection is utilized. When utilizing a heating and flushing gas which does not support combustion, the gas may be suiciently hot to heat the section of stratum to a temperature above ignition temperature of the carbonaceous material. When heating the section of stratum around the ignition borehole by a radiant downhole heat source, such as a heater, it is feasible to heat the formation over an extended period without injecting ushing gas until the temperature of the section of stratum is in the range of about 300 F. to the ignition temperature of the hydrocarbon material in the stratum (about 500 to 600 F.) and thereafter injecting non-combustion supporting flushing fluid into the section of stratum so as to drive the viscous liquid hydrocarbon material therefrom. After driving the viscous hydrocarbon into the ignition borehole, the same may be removed by means of a pump or bucket or all or any portion of it may be burned in the hole in order to further heat the surrounding section of stratum and raise the same to ignition temperature for the ignition step effected by introducing combustion supporting gas thereinto.

A more complete understanding of the invention may be obtained by reference to the accompanying schematic drawing of which FIGURES 1 and 2 are elevations thru an oil or tar bearing stratum showing well or borehole positions and arrangement of some equipment for effecting the invention.

Referring to the drawing a central well or borehole is surrounded by a plurality of wells or boreholes 12. Each of the wells is provided with tubing or conduit 14 for injecting or withdrawing fluids from the boreholes. Central well 10 is shown provided with a downhole heater 16. Each of the boreholes penetrates permeable carbonaceous stratum 18. In FIGURE l, the preheated area surrounding ignition well 10 is identified by numeral 2t) and the preheated section of the stratum around borehole 1t) in FIGURE 2 is identified by numeral 22. Sections and 22 represent either heated areas from which heavy liquid hydrocarbons have been flushed or solvent extracted areas.

ln the embodiment of the invention illustrated in FIG- URE l, the section 20 around ignition well 10 is heated by a gas tired or electric heater 16 and air is injected into formation 18 thru auxiliary wells 12 spaced a substantial distance from well 10, either in a ring pattern with well 10 centrally located or in-line on either side of a series of in-line wells 10. The heating of section 20` is continued until the temperature thereof is in the range of 300 F. to just below the ignition temperature of the hydrocarbon therein thereby rendering more uid or melting the tar present in the stratum in section 20. The injected air passes thru the heated section 20 and flushes the liquid tar or other highly viscous hyrocarbon into well 10 from which it is removed by any suitable means or method. lt is preferred to heat section 20 to the desired temperature for fiuidizing and removing the heater 16 before flushing the liquid hydrocarbon from the heated section and burning the melted tar in borehole 10, either as it arrives therein or after the ushing step is well under way or completed.

The heating and ushing are controlled so as to leave sufficient residual hydrocarbon material in section 20 to provide adequate fuel for in situ combustion and movement of the combustion front thru this section of stratum to the surrounding stratum. When the ushing step is completed, the temperature of section 20 is raised either by burning the liquid hydrocarbon in borehole 10 or by removing the same and positioning downhole heater 16 in heating position and again applying heat to section 20 so as to raise the temperature thereof to suitable ignition temperature. Oxygen-containing gas is then injected li either thru wells 12 or well 10 so as to ignite the stratum in section 20 and establish in situ combustion. ln the event injection of air thru well 10 is utilized i or initiating combustion, the flow of air is cut off to this well after a substantial combustion zone has been established and injection of air thru boreholes 12 is utilized to feed the combustion Zone and move the same outwardly from borehole 10 by inverse movement of air. If air is injected initially thru boreholes 12 to initiate combustion in section 20, reversal of air flow is not required since the combustion zone will progress outwardly from well 10 to wells 12. When the combustion zone reaches wells 12, injection may be initiated thru an outer ring of wells so as to continue the movement of the combustion zone thru the stratum toward the outer ring of wells. By continuing the injection of air thru wells 12 while injecting from an outer ring of wells, a combustion zone can be moving outwardly from wells 12 and another one inwardly toward well 10 with the combustion in the latter feeding on the residual carbon produced in the stratum intermediate wells 12 and 10 by the first burning wave effected by inverse air injection thru wells 12. Produced hydrocarbons and combustion gases are usually recovered thru well 10 which is a production well, but production may be recovered thru wells 12 after the combustion zone passes beyond these wells.

The embodiment of the invention illustrated in FIG- URE 2 comprises heating section 22 intermediate wells 10 and 12 by any suitable means, such as heater 16, and injecting flushing 'liuid thru well 10 to drive liquefied hydrocarbons from section 22 into auxiliary wells 12 from which the liquid hydrocarbon is recovered by any suitable means. in the embodiment shown in FIGURE 2, wells 12 are spaced more closely to well 10 than in the embodiment shown in FlGURE l, this spacing being in the range of about 2 to 25 feet. After initiation of combustion in section 22 in accordance with the invention as described hereinbefore and advancement of the combustion zone to the vicinity of wells 12, injection from an outer ring of wells is utilized to move the combustion front further thru the formation. It is also feasible to position a series of ignition wells along a line intermediate parallel rows of auxiliary wells 12 and effect the flushing and in situ combustion in similar manner to that described in connection with FIGURES 1 and 2. Where the permeability of the stratum is low it may be desirable to horizontally fracture and prop the same in conventional manner.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

I claim:

l. A process for initiating in situ combustion in a permeable stratum containing hydrocarbon material which forms a highly viscous liquid upon heating, which comprises heating a section of said stratum around an ignition borehole therein to an elevated temperature below the ignition temperature 0f the hydrocarbon material so as to render said material more uid; passing a flushing uid thru said section between said ignition borehole and an offset borehole in said stratum so as to move `said viscous liquid to one of said boreholes; removing the flushed out liquid; thereafter initiating combustion in said section of stratum around Isaid ignition borehole; and feeding free oxygen to the resulting combustion zone so as to drive said Zone outwardly from said borehole thru and stratum.

2. A process for initiating in situ combustion in a permeable stratum containing hydrocarbon material which forms a highly viscous liquid upon heating, which comprises heating a section of said stratum around an ignition borehole therein so as to render said material more Huid; passing a non-combustion supporting flushing fluid thru said section between said ignition borehole and an offset borehole in said lstratum so as to move said viscous liquid to one of said boreholes; removing the ushed out liquid; thereafter initiating combustion in said section of stratum around said ignition borehole; and feeding free oxygen to the resulting combustion zone so as to drive said zone outwardly from said borehole thru said stratum.

3. The process of claim 1 wherein said ilushing gas is air, said flushing `step and same is contacted with free oxygen while at said temperature so as to effect the ignition step.

4. The process of claim l wherein the ushing uid is passed thru said section of stratum from said olset borehole to said ignition borehole.

5. The process of claim 4 wherein the viscous hydrocarbon ushed into said ignition borehole is ignited and burned therein so as to heat said section of stratum to ignition temperature yand free oxygen is passed thru said said stratum from said offset borehole to said ignition borehole to initiate combustion Within said stratum.

6. The process of claim 1 wherein said flushing fluid is passed thru said section of stratum from said ignition borehole to at least one borehole spaced therefrom within the range of about 2 to 25 feet.

7. The process of claim 6 wherein heating of said section of Stratum is continued thru said ignition borehole after the flushing step so as `to raise said section to the ignition temperature and said section is contacted with free oxygen while at said temperature to initiate combustion of said hydrocarbon material.

8. A process for initiating in situ combustion in a permeable stratum containing hydrocarbon material which forms a highly viscous liquid upon heat-ing said stratum, which comprises heating a section `of said stratum around lan ignition borehole therein to a temperature above about 300 F. but below ignition temperature of said material in contact with air by applying heat to the walls of said borehole and injecting air thru said borehole into said stratum and withdrawing same -thru a plurality of boreholes positioned in -a ring pattern around said ignition borehole closely spaced therefrom, whereby highly viscous hydrocarbon material is flushed into said boreholes; removing said viscous material from said boreholes; thereafter continuing the heating step so as to raise the temperature of said section to ignition temperature; `and contacting said section with air so as to ignite same and establish in situ combustion therein` 9. The process of claim 8 wherein the Iair for the ignition -step is injected thru said boreholes and combustion gas and produced hydrocarbons are withdrawn thru said ignition borehole.

10. The process of claim 8 wherein the air for the ignition step is injected thru said ignition borehole and combustion gases and produced hydrocarbons are withdrawn thru said boreholes.

11. The process of claim 8 wherein heat lfor the initial Iheating step is supplied by injecting lhot air as ushing gas.

l2. A process for initiating in situ combustion in a permeable stratum containing hydrocarbon material which forms a highly viscous liquid upon heating said stratum, which comprises heating a section of said stratum around van ignition borehole therein to a temperature above about 300 F. but below ignition temperature of said material in contact with air by applying heat to Ithe walls of said borehole 4and injecting air thru a plurality of boreholes .positioned in a ring pattern around said ignition borehole and withdrawing same thru said ignition borehole, whereby highly viscous hydrocarbon material is flushed into said ignition borehole; removing said material from said borehole; thereafter continuing the heating step so as to raise the temperature of said section to ignition temperature; and contacting lsaid section with air so as to ignite -sa-rne `and establish in situ combustion therein.

13. The process of claim 12 wherein heat is applied to the wall of said ignition borehole by a downhole heater, said heater is removed 'after the llushing step, said viscous material is removed from said borehole by burning same therein to heat said section to ignition ternperature, and ignition is eiect-ed by injecting air thru said boreholes so Ias to force sarne toward said ignition borehole.

References Cited in the le of this patent UNITED STATES PATENTS 1,520,012 Conrader Dec. 23, 1924 2,300,348 Dana Oct. 27, 1942 2,584,606 Merriam Feb. 5, 1952 2,670,047 Mayes May 23, 1954 2,793,696 Morse May 28, 1957 2,906,337 Hennig Sept. 29, 1959 November 6, 1962 Patent No7 3,062,282

Arthur IL, Schleicher he above numbered patt error appears in t Ratent should read as It is hereby certified tha said Letters ent requiring correction and that the corrected below.

after "said" insert section of Column 5, line 8,

rting temperature after stratum is heated to combustion-suppe the n. I

Signed and sealed this 3rd day of September l963 (SEAL) Attest:

' DAVID L. LADD ERNEST W. SWIDEF.

Commissioner of Patents Attesting Officer 

1. A PROCESS FOR INITIATING IN SITU COMBUSTION IN A PERMEABLE STRATUM CONTAINING HYDROCARBON METERIAL WHICH FORMS A HIGHLY VISCOUS LIQUID UPON HEATING, WHICH COMPRISES HEATING A SECTION OF SAID STRATUM AROUND AN IGNITION BOREHOLE THEREIN TO AN ELEVATED TEMPERATURE BELOW THE IGNITION TEMPERATURE OF THE HYDROCARBON MATERIAL SO AS TO RENDER SAID MATERIAL MORE FLUID; PASSING A FLUSH ING FLUID THRU SAID SECTION BETWEEN SAID IGNITION BOREHOLE AND AN OFFSET BOREHOLE IN SAID STRATUM SO AS TO MOVE SAID VISCOUS LIQUID TO ONE OF SAID BOREHOLES; REMOVING THE FLUSHED OUT LIQUID; THEREAFTER INITIATING COMBUSTION IN SAID SECTION OF STRATUM AROUND SAID IGNITION BOREHOLE; AND FEEDING FREE OXYGEN TO THE RESULTING COMBUSTION ZONE SO AS TO DRIVE SAID ZONE OUTWARDLY FROM SAID BOREHOLE THRU AND STRATUM. 